// Copyright (c) Microsoft Open Technologies, Inc. All rights reserved. See License.txt in the project root for license information.

#pragma once

/*! \file rx-merge.hpp

    \brief For each given observable subscribe.
           For each item emitted from all of the given observables, deliver from the new observable that is returned.

           There are 2 variants of the operator:
           - The source observable emits nested observables, nested observables are merged.
           - The source observable and the arguments v0...vn are used to provide the observables to merge.

    \tparam Coordination  the type of the scheduler (optional).
    \tparam Value0  ... (optional).
    \tparam ValueN  types of source observables (optional).

    \param  cn  the scheduler to synchronize sources from different contexts (optional).
    \param  v0  ... (optional).
    \param  vn  source observables (optional).

    \return  Observable that emits items that are the result of flattening the observables emitted by the source observable.

    If scheduler is omitted, identity_current_thread is used.

    \sample
    \snippet merge.cpp threaded implicit merge sample
    \snippet output.txt threaded implicit merge sample

    \sample
    \snippet merge.cpp implicit merge sample
    \snippet output.txt implicit merge sample

    \sample
    \snippet merge.cpp merge sample
    \snippet output.txt merge sample

    \sample
    \snippet merge.cpp threaded merge sample
    \snippet output.txt threaded merge sample
*/

#if !defined(RXCPP_OPERATORS_RX_MERGE_HPP)
#define RXCPP_OPERATORS_RX_MERGE_HPP

#include "../rx-includes.hpp"

namespace rxcpp {

namespace operators {

namespace detail {

template<class... AN>
struct merge_invalid_arguments {};

template<class... AN>
struct merge_invalid : public rxo::operator_base<merge_invalid_arguments<AN...>> {
    using type = observable<merge_invalid_arguments<AN...>, merge_invalid<AN...>>;
};
template<class... AN>
using merge_invalid_t = typename merge_invalid<AN...>::type;

template<class T, class Observable, class Coordination>
struct merge
    : public operator_base<rxu::value_type_t<rxu::decay_t<T>>>
{
    //static_assert(is_observable<Observable>::value, "merge requires an observable");
    //static_assert(is_observable<T>::value, "merge requires an observable that contains observables");

    using this_type = merge<T, Observable, Coordination>;

    using source_value_type = rxu::decay_t<T>;
    using source_type = rxu::decay_t<Observable>;

    using source_operator_type = typename source_type::source_operator_type;
    using value_type = typename source_value_type::value_type;

    using coordination_type = rxu::decay_t<Coordination>;
    using coordinator_type = typename coordination_type::coordinator_type;

    struct values
    {
        values(source_operator_type o, coordination_type sf)
            : source_operator(std::move(o))
            , coordination(std::move(sf))
        {
        }
        source_operator_type source_operator;
        coordination_type coordination;
    };
    values initial;

    merge(const source_type& o, coordination_type sf)
        : initial(o.source_operator, std::move(sf))
    {
    }

    template<class Subscriber>
    void on_subscribe(Subscriber scbr) const {
        static_assert(is_subscriber<Subscriber>::value, "subscribe must be passed a subscriber");

        using output_type = Subscriber;

        struct merge_state_type
            : public std::enable_shared_from_this<merge_state_type>
            , public values
        {
            merge_state_type(values i, coordinator_type coor, output_type oarg)
                : values(i)
                , source(i.source_operator)
                , pendingCompletions(0)
                , coordinator(std::move(coor))
                , out(std::move(oarg))
            {
            }
            observable<source_value_type, source_operator_type> source;
            // on_completed on the output must wait until all the
            // subscriptions have received on_completed
            int pendingCompletions;
            coordinator_type coordinator;
            output_type out;
        };

        auto coordinator = initial.coordination.create_coordinator(scbr.get_subscription());

        // take a copy of the values for each subscription
        auto state = std::make_shared<merge_state_type>(initial, std::move(coordinator), std::move(scbr));

        composite_subscription outercs;

        // when the out observer is unsubscribed all the
        // inner subscriptions are unsubscribed as well
        state->out.add(outercs);

        auto source = on_exception(
            [&](){return state->coordinator.in(state->source);},
            state->out);
        if (source.empty()) {
            return;
        }

        ++state->pendingCompletions;
        // this subscribe does not share the observer subscription
        // so that when it is unsubscribed the observer can be called
        // until the inner subscriptions have finished
        auto sink = make_subscriber<source_value_type>(
            state->out,
            outercs,
        // on_next
            [state](source_value_type st) {

                composite_subscription innercs;

                // when the out observer is unsubscribed all the
                // inner subscriptions are unsubscribed as well
                auto innercstoken = state->out.add(innercs);

                innercs.add(make_subscription([state, innercstoken](){
                    state->out.remove(innercstoken);
                }));

                auto selectedSource = state->coordinator.in(st);

                ++state->pendingCompletions;
                // this subscribe does not share the source subscription
                // so that when it is unsubscribed the source will continue
                auto sinkInner = make_subscriber<value_type>(
                    state->out,
                    innercs,
                // on_next
                    [state, st](auto&& ct) {
                        state->out.on_next(std::forward<decltype(ct)>(ct));
                    },
                // on_error
                    [state](rxu::error_ptr e) {
                        state->out.on_error(e);
                    },
                //on_completed
                    [state](){
                        if (--state->pendingCompletions == 0) {
                            state->out.on_completed();
                        }
                    }
                );

                auto selectedSinkInner = state->coordinator.out(sinkInner);
                selectedSource.subscribe(std::move(selectedSinkInner));
            },
        // on_error
            [state](rxu::error_ptr e) {
                state->out.on_error(e);
            },
        // on_completed
            [state]() {
                if (--state->pendingCompletions == 0) {
                    state->out.on_completed();
                }
            }
        );
        auto selectedSink = on_exception(
            [&](){return state->coordinator.out(sink);},
            state->out);
        if (selectedSink.empty()) {
            return;
        }
        source->subscribe(std::move(selectedSink.get()));
    }
};

}

/*! @copydoc rx-merge.hpp
*/
template<class... AN>
auto merge(AN&&... an)
    ->     operator_factory<merge_tag, AN...> {
    return operator_factory<merge_tag, AN...>(std::make_tuple(std::forward<AN>(an)...));
}

}

template<>
struct member_overload<merge_tag>
{
    template<class Observable,
        class Enabled = rxu::enable_if_all_true_type_t<
            is_observable<Observable>>,
        class SourceValue = rxu::value_type_t<Observable>,
        class Merge = rxo::detail::merge<SourceValue, rxu::decay_t<Observable>, identity_one_worker>,
        class Value = rxu::value_type_t<SourceValue>,
        class Result = observable<Value, Merge>
    >
    static Result member(Observable&& o) {
        return Result(Merge(std::forward<Observable>(o), identity_current_thread()));
    }

    template<class Observable, class Coordination,
        class Enabled = rxu::enable_if_all_true_type_t<
            is_observable<Observable>,
            is_coordination<Coordination>>,
        class SourceValue = rxu::value_type_t<Observable>,
        class Merge = rxo::detail::merge<SourceValue, rxu::decay_t<Observable>, rxu::decay_t<Coordination>>,
        class Value = rxu::value_type_t<SourceValue>,
        class Result = observable<Value, Merge>
    >
    static Result member(Observable&& o, Coordination&& cn) {
        return Result(Merge(std::forward<Observable>(o), std::forward<Coordination>(cn)));
    }

    template<class Observable, class Value0, class... ValueN,
        class Enabled = rxu::enable_if_all_true_type_t<
            all_observables<Observable, Value0, ValueN...>>,
        class EmittedValue = rxu::value_type_t<Observable>,
        class SourceValue = observable<EmittedValue>,
        class ObservableObservable = observable<SourceValue>,
        class Merge = typename rxu::defer_type<rxo::detail::merge, SourceValue, ObservableObservable, identity_one_worker>::type,
        class Value = rxu::value_type_t<Merge>,
        class Result = observable<Value, Merge>
    >
    static Result member(Observable&& o, Value0&& v0, ValueN&&... vn) {
        return Result(Merge(rxs::from(o.as_dynamic(), v0.as_dynamic(), vn.as_dynamic()...), identity_current_thread()));
    }

    template<class Observable, class Coordination, class Value0, class... ValueN,
        class Enabled = rxu::enable_if_all_true_type_t<
            all_observables<Observable, Value0, ValueN...>,
            is_coordination<Coordination>>,
        class EmittedValue = rxu::value_type_t<Observable>,
        class SourceValue = observable<EmittedValue>,
        class ObservableObservable = observable<SourceValue>,
        class Merge = typename rxu::defer_type<rxo::detail::merge, SourceValue, ObservableObservable, rxu::decay_t<Coordination>>::type,
        class Value = rxu::value_type_t<Merge>,
        class Result = observable<Value, Merge>
    >
    static Result member(Observable&& o, Coordination&& cn, Value0&& v0, ValueN&&... vn) {
        return Result(Merge(rxs::from(o.as_dynamic(), v0.as_dynamic(), vn.as_dynamic()...), std::forward<Coordination>(cn)));
    }

    template<class... AN>
    static operators::detail::merge_invalid_t<AN...> member(AN...) {
        std::terminate();
        return {};
        static_assert(sizeof...(AN) == 10000, "merge takes (optional Coordination, optional Value0, optional ValueN...)");
    }
};

}

#endif
